EVOLUTION OF THE ARCTIC ALASKA-CHUKOTKA MICROPLATE FROM DETRITAL ZIRCON ANALYSIS OF CRETACEOUS SEDIMENTS OF THE NORTH SLOPE, ALASKA, AND JURA-CRETACEOUS PLUTONS AND SEDIMENTS OF CHUKOTKA, RUSSIA

The timing of rotation of the Arctic Alaska-Chukotka microplate (AACM) from the Canadian Arctic Islands to its current position remains one of the largest unsolved questions about the opening of the Canada Basin, Arctic Ocean, with estimates from Jurassic to Paleocene, and most suggesting rifting in the Early Cretaceous. Along the northern margin of the AACM, the Colville Basin was filled from 115 to 95 Ma during eastward progradation of the Corwin Delta, represented by the Aptian-Albian-Cenomanian Torok and Nanushuk Formations. To better understand source to sink relations in the area during this time period, we analyzed three samples from the Torok and Nanushuk for detrital zircon U-Pb ages and Hf isotopic ratios to compare to the ages and Hf ratios of 15 plutons in Chukotka/NE Russia, the Jura-Cretaceous clastic strata they intrude, and older analyzed Triassic sedimentary rocks, all constituting the inferred source region for the Colville Basin.

The 110 to 95 Ma ages and Hf ratios (εHf = -14 to +4) of the youngest zircons in the Colville Basin match those of plutons in Chukotka that were emplaced during regional extension, uplift and erosion. Jurassic zircons in the Colville Basin and Chukotka Jura-Cretaceous clastic strata have a range of more evolved Hf ratios (εHf = -20 to +8) in contrast to the Hf ratios of Jurassic zircons derived from the erosion of the Angayucham terrane in the adjacent Brooks Range (εHf = +10 to +15). Specifically, the Hf ratios of 160 to 130 Ma zircons in Jurassic Chukotka clastic strata and the Colville strata are compatible with derivation from the Main and Northern plutonic belts of NE Russia, nearly 2,500 km to the west of the Colville Basin. Additionally, the presence of 550 to 400 Ma zircon in the Colville Basin requires the recycling of Triassic sediments from Chukotka/NE Russia, as previously reported. These findings suggest the bulk of the Aptian-Albian-Cenomanian sediment fill of the Colville Basin was derived from westward sources in Chukotka/NE Russia in a continental-scale sediment routing system. It is also possible that these paleogeographic linkages between source and sink may have been disrupted by the opening of the Amerasia Basin, or by the opening of the Canada Basin, after the deposition of the Torok and Nanushuk Formations.